Diseases related to the cardiovascular area includes quantitative abnormalities of the degree of progress of lesion due to arteriosclerotic hypertrophy, and abnormalities such that a fibrous membrane at the surface of atheroma called vulnerable plaque which is thin and brittle comes to rupture to cause thrombus, bleeding, stenosis or occlusion, leading to crisis of stenocardia, myocardial infarction or cerebral infarction.
Vulnerable plaque cannot be checked under a radiography. Therefore, to check vulnerable plaque, the intended blood vessel is determined by use of OCT (optical coherence tomography) or the like. Using OCT or the like, the location of the vulnerable plaque is determined using data on the distance between the vulnerable plaque and a nearest bifurcated blood vessel, the distance between the vulnerable plaque and a stent previously left indwelling, or the like.
To cure a lesion such as plaque, a stenosed lesion, an occluded lesion, etc. generated in a blood vessel or other lumen in vivo, a stent is left indwelling in the lesion to maintain patency of the lumen.
Since the stent is inserted in vivo from the exterior, the stent is small in diameter at the time of insertion. The stent is enlarged in diameter through expansion in the stenosed lesion or the occluded lesion and maintains patency of the lumen.
The stents that are generally used include hollow cylindrical stents obtained by processing metallic wire or metallic pipe. The stent is mounted on a catheter or the like while in a reduced diametrical size, and is then inserted in vivo, and is expanded in a target lesion by a known method to come into close contact with and be fixed on the inner wall of the target lesion (lumen), thereby maintaining patency of the lumen. The stents are classified into self-expandable stents and balloon-expandable stents according to function and method of indwelling. A balloon-expandable stent is a stent which itself does not have an expanding function. Instead, after the stent mounted on a balloon is inserted into a target lesion, the balloon is dilated so that the stent is expanded (plastically deformed) by the expanding (dilating) force of the balloon to come into close contact with and be fixed on the inner surface of the target lumen. This type of stent needs the just-mentioned stent-expanding work. On the other hand, a self-expandable stent is a stent which itself is provided with an expanding function. This type of stent is inserted in vivo in the state of being compressed to a smaller diametrical size, and is released in a target lesion from the compression to return into its initial expanded state and to come into close contact with and be fixed on the inner wall of the target lumen, thereby maintaining patency of the lumen.
The purpose of indwelling a stent at present is for returning a stenosed blood vessel into its original patency, and mainly for preventing restenosis which might otherwise occur after such a procedure as PTCA is conducted. In recent years, stents have come to be used for ameliorating a lesion (plaque) which will highly probably become a stenosed region.
The self-expandable stents are mostly used in peripheral regions such as blood vessels in femoral and carotid arteries, and include, for example, those having a form as shown in JP-T-H11-505441.
Another self-expandable stent is shown in Japanese Patent Laid-Open No. 2008-272374. A stent delivery system 1 according to Japanese Patent Laid-Open No. 2008-272374 includes a distal-side tube 2, a proximal-side tube 4 fixed to a proximal portion of the tube 2, a stent accommodating tubular member 5 which can be slid in the proximal direction, a self-expandable stent 3 accommodated in the stent accommodating tubular member 5, and a pulling traction wire 6 for moving the stent accommodating tubular member 5 toward the proximal side. The stent accommodating tubular member 5 is moved on the outer surface of a fixed tube 8 toward the proximal side by pulling the wire 6. The stent accommodating tubular member 5 has a tubular proximal member 54 made of a hard material which is fixed to the proximal end of the stent accommodating tubular member 5 and has an inner surface making contact with the outer surface of the fixed tube 8 when the stent accommodating tubular member 5 is moved toward the proximal side.
In the case where a stent delivery system which uses a self-expandable stent proposed in JP-T-H11-505441 and Japanese Patent Laid-Open No. 2008-272374 is used and the stent is positioned in the lesion (e.g., plaque forming), the position of a vulnerable plaque is determined, before insertion of the delivery system, by way of the distance between the vulnerable plaque and an indicator such as the nearest bifurcated blood vessel, a stent previously left indwelling, etc. by use of the above-mentioned OCT.
Then, the stent accommodating part of the delivery system is inserted in the determined lesion, and thereafter the stent is discharged, whereby the stent is indwelled in the lesion.
However, the self-expandable stent has difficulties in that its initial positioning for indwelling must be conducted accurately, since the stent restores its original shape by its own expanding force once it is discharged. In addition, in many cases, the self-expandable stent itself is not clearly confirmed under radiography. Besides, the plaque forming lesion cannot be checked under radiography while the delivery system is set indwelling in the lesion.